Astronauts working to bring to life a new 17½-ton solar panel addition to the international space station lost another screw to the void Wednesday but made it through a successful if arduous spacewalk.

In a 7-hour, 11-minute spacewalk — nearly 45 minutes longer than planned — Dan Burbank and Steve MacLean of the Canadian Space Agency connected the solar arrays and prepared the structure's joint for an inaugural rotation later in the day.

Once the solar arrays are operating, the rotating joint will move with the sun to maximize the amount of power generated. They eventually will supply a quarter of the space lab's power when it is completed by 2010.

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The spacewalking duo's construction shift was not without incident.

The astronauts had to remove more than a dozen insulation covers and scores of bolts while wearing bulky spacesuit gloves, and the work wasn't easy.

One stuck bolt on a launch restraint slowed down the process. The astronauts struggled together to get it loose, with astronaut Joe Tanner, inside the space station, helping out.

"We sure appreciate you answering that age-old question from Mission Control — how many astronauts does it take to unscrew a bolt," said astronaut Pam Melroy in Mission Control in Houston. "Apparently, it takes three. Two outside and one inside."

While MacLean was removing a cover on a crucial rotary joint, one of the four bolts he had for the task disappeared. Another bolt had escaped during a spacewalk Tuesday.

"I did not see it go," MacLean said.

Space debris can be dangerous if it punctures space station walls or spacesuits and can jam crucial mechanisms.

However, spacewalkers have a long history of losing things in space. In July, Discovery spacewalkers lost a 14-inch spatula that floated away.

There was no indication that the latest missing bolt went into the rotary joint or any other space station mechanisms, and the assumption is it floated away, NASA spokesman Grey Hautaluoma said.

He said that the astronauts simply used three bolts for the task instead of four, and that there shouldn't be a problem with that.

MacLean ran into another small problem a short time later when an extension on his pistol-grip power tool broke while he was trying to remove a restraint on the rotary joint.

"Son of a gun," he muttered, then gathered the pieces in a trash bag so they wouldn't float away and went to a toolbox to retrieve another.

Tanner and Heidemarie Stefanyshyn-Piper, who conducted the first spacewalk, planned to return for the third and final spacewalk on Friday.

Before the mission, NASA managers and the astronauts had warned that the three planned spacewalks to hook up the new $372 million addition to the space station during Atlantis' 11-day mission could be difficult.

"What they're doing is so extremely critical, but very repetitive," Tanner said before the mission. "We will work hard at not getting lulled into boredom or complacency."

Both Burbank and MacLean made their spacewalk debuts this week.

"I just don't want to be real clumsy," Burbank said before the mission. "The first thing I'm going to do is go slow and ease my way into it."

To pump them up for the hard work ahead, Mission Control played "Takin' Care of Business" as their wake-up song.

[The selection, by Canadian hard-rock band Bachman-Turner Overdrive, may also have been a salute to MacLean's nationality.]

Engineers have determined that Atlantis' heat shield is in such good shape — free from the type of the damage that led to Columbia's disintegration — that it is clear for landing at the end of its scheduled mission next Wednesday.

MacLean, in his spacewalk debut, got a chance to informally inspect the shuttle's underside when he posed for a spacewalking photo.

"That's about as photogenic as I get," he said.